Recovery of cellulose esters from scrap



Patented Nov. 16, 1937 UNITED STAT S RECOVERY OF CE ULOSE ESTERS FROM R SOAP Marvin J. Reid, Rochester, N. Y., asslgnor to Eastman Kodak Com pany, Rochester, N. Y., a

corporation of New Jersey No Drawing. Applica tion February 10, 1937,

Serial No. 125,116

8 Claims.

This application relates to the recovery of an organic acid ester of cellulose which has been used as the base for photographic film from the scrap film by means of a mixture of acetone and a lower 5 aliphatic alcohol.

Photographic film is composed of a photosensitive gelatin emulsion supported by a reenforcing layer commonly referred to as the film base. Often the film base needs to be overcoated or subbed with a layer of material to promote the adhesion of the photosensitive emulsion thereto. Also, with some types of film it is desirable that the base or the subbing layer or both be tinted to give desired effects or to prevent halation or both. When photographic film is scrapped, it is desirable to recover the organic acid ester of cellulose, which is used as the base of the film. To do this requires the removal of the photosensitive emulsion and of the subbing layers and the tinting material which has been employed therewith. In some cases additional layers are put on, such as to still further increase the adhesiveness of the emulsion to the film base.

Various methods have been proposed for removing these additional materials which are employed with a film base to prepare photographic film. For instance, for the removal of the color from tinted film the combination of bleaching and washing has been suggested, however, by this process small amounts of impurities are left in the film support which are injurious to some types of photosensitive emulsions and, therefore, the use of the scrap, recovered by this means, is restricted.

I have found that a mixture of acetone and an 0 aliphatic alcohol, consisting predominately of the latter, is eminently suited to the removal of the subbing layers used on film base comprising organic acid esters of cellulose and to the substantially complete removal of the tinting material 40 from a tinted film base. A mixture, which has been found to be generally suitable, consists of 85% of the lower aliphatic alcohol particularly methyl alcohol and 15% acetone, although the proportion of acetone may range from 10-20% 45 and still form a leaching liquid which is quite satisfactory.

The subbing material which is commonly employed on film base consisting of an organic acid ester of cellulose is either a resin of the synthetic type, such as a bakelite resin or one of the polyvinyl resins or an organic acid ester of cellulose which has been hydrolyzed much further than the organic acid ester of cellulose which is employed for the film base. As an example of recovering the ester from scrap film, the scrap is comminuted and washed with warm water to remove the emulsion and any gelatin coatings thereon. It is then leached with a mixture of the alcohol and acetone, preferably in a counter-current system. After the subbing layers and tinting have been sufficiently removed, the scrap is then washed with water to thoroughly remove the solution and recover it from the scrap. The support is then dried and kept stored for future use in the preparation of solutions for making colloidized products. Obviously, if the base is made from an ester which has been hydrolyzed considerably, the acetone-alcohol mixture might soften the base to too great an extent. At the present time, however, the film base, which is ordinarily used, is of a type which will not be affected by the alcoholacetone mixture and, therefore, my invention is eminently suited for the recovery of that type of film. The organic acid ester of cellulose subbing layers may be composed of either hydrolyzed cellulose acetate, cellulose acetate propionate or cellulose acetate butyrate which has been hydrolyzed considerably beyond the point where the hydrolysis to obtain an ester suitable for making the film base is usually stopped.

In photographic film the subbing layer and the tintjoin' themselves very closely to the film base and almost seem to penetrate into the pores I thereof. Therefore, a rather severe treatment is necessary to remove the tinting material and the hydrolyzed ester which has been employed as the sub. I have found that by the incorporation of a small amount of acetone, the mixture formed is especially adapted to rendering the impurities more susceptible to removal by the leaching solvent, particularly as the acetone seems to exert a swelling action on the film base.

The following examples illustrate the application of my invention to difierent types of photographic film scrap.

Ewample I Approximately 250 pounds (dry weight) of photographic film scrap, having a base of cellulose acetate and a subbing layer of a cellulose 45 acetate which has been hydrolyzed to 25-30% acetyl, was chopped into pieces about 2 in. square and then soaked in warm water at 110 F. for 24 hours and was then washed in several changes of warm Water at 110 F. The scrap was then 5 leached in an agitated jacketed vessel using three one hour changes of a solution of methyl alcohol-acetone (85:15) at 80100 F. The scrap was wet when treated with the mixture, however,

1 the first treatment the amount of water presv55 nomical operation of the process.

ent was not more than while with the second step, the amount of water was below 15% and for the third step, the water had decreased to 5%. can be tolerated in the process, hence it is undesirable to use scrap which is intoov wet a condition. The solvent was used counter-currently on successive batches in order to make for ecothird treatment, the recovered scrap was separated from the leaching'liduid and thoroughly washed with water to remove the solvent after which it was dried. As amatter ofeconomy, it is also desirable to carry out the washing of the scrap with water in a counter-current system; After the recovered scrap is, dried, it can be stored and employed in making up solutions alone or with additional fresh material.

Example II Approximately 250 pounds of photographic film scrap, having a film base of cellulose acetate and a subbing layer of a Bakelite resin, was comflminuted and washed with warm water to remove It was then leached lite resin, it may be of some other synthetic resin. Both the subbing layer 7 andthe. tinting material, if any is present, is removed by this treatment. A r

Example III Cellulose acetate film support subbed with gelatin containing a blue dye and coated with an emulsion was chopped into small pieces and washed in warm water to remove the emulsion and gelatin coatings therefrom. The dye had penetrated the cellulose acetate base and this dye was not removed by the warm water washing. About 500 pounds of this wet, washed film scrap was added to 750 gals. of methyl alcoholacetone (85:15) and the mass was agitated for one hour while maintaining-a temperature of 100 F. The solution was withdrawnandthe scrap was again treated witha second 750- gals. of a like mixture of methyl alcohol and acetone, being agitated for the same time and at the same temperature. This treatment was repeated making three one hour treatments in-all. The scrap was then washed in several changes of water and I was then dried and stored for use in making cellulose acetate dope solutions.

The solution of. methylalcohol and acetone softens and swells the support at 100 F. sufficiently so that the tinting material can be satisfactorily removed therefrom but not to such a degree that the scrap cannot be safely agitated.

This swelling and softening can be controlled by varying the temperature of the solution so that, .if the removal of the tinting material, is not as 'complete as desirable, the temperature may be greater, while if the solvent is causing so much 'swelling that the'scrap will not stand up after agitation in the solution, a temperature 'of'less 1 degree is then desirable for maximum results;

'My invention is not limited to the use of methyl alcohol as otherlower aliphatic alcohols These water contents are the most that After the may be employed in admixture with acetone to recover film scrap. Ethyl alcohol may be employed as the lower aliphatic alcohol in which case it is preferable that more acetone be employed to give sufficient swelling action. This is because ethyl alcohol alone appears to have practically no swelling action on cellulose acetate or the other organic acid esters of cellulose. Mixtures of isopropyl alcohol and acetone are very satisfactory for the recovery of organic 'acid esters of cellulose from scrap film. Butyl alcohol-acetone might be employed but has the disadvantageof thelow solubility of the butyl alcohol in water. As the Water insolubility of the alcohols increases beyond the alcohols of 4 carbon atoms thispoint may be considered the practical limit of the alcohol constituent.

My process is applicable to the usual type of film base prepared from the lower fatty acid estersof cellulose, such as. cellulose acetate or cellulose acetate. propionate or acetate butyrate. Obviously if the. e ter employed in preparing the film base should be so susceptible to the action of the methyl alcohol-acetone mixturethat it softens to .an appreciable degree, my processwould not give the best results therewith,-although it could be employed.

In addition tothe subbinglayers and the tint- ;ing materials which are'employed in the photographicfllmswith the cellulose esters, plasticizers. are also usually present. My recovery process has the-advantagethat italso removes practically all of the plasticizer from the ester. Also, if'nitrocellulose subbing layers are present in. the scrap film, that material is also removed .in my process for recoveflng film scrap.

=.I. claimz- -1..A method for recovering photographic film having a base of'a. lower organic acid ester of cellulose which comprises washing the film scrap .with warm water, then leaching it with a mixture of a lower aliphatic alcohol and acetone, in proportions which will swell the cellulose ester, at atemperature of 68-110-"- F. under conditions whereby thescrap. is not greatly softened and then washing the scrap to remove the leaching solution therefrom.

I '2. A method of recovering photographic film having a cellulose acetate base which comprises -washing the film scrap with warm water, then leaching it with amixture of a lower aliphatic alcohol and acetone, in proportions which will swell the cellulose'acetate, at 'a temperature of 63-l10 F.'under conditions whereby the scrap is not greatly softened and then washing the scrap to remove the leaching solution therefrom.

3. A method forrecovering photographic film scrap having a baseof a lower organic acid ester of cellulose which comprises washing the film scrap with warm water, then leaching it with a mixture of methyl alcohol and acetone containing 10-20% of the latter, at 68-110 F. under conditions whereby the scrap is not greatly sofder conditions whereby the scrap is not greatly softened, then washing the scrap to remove the leaching solution therefrom.

5. A method for recovering photographic film scrap having a cellulose acetate base which comprises washing the film scrap with warm water, then leaching it with a mixture of methyl alcohol and acetone containing 10-20% of the latter, at 68-110 F. under conditions whereby the scrap is not greatly softenedvand then washing the scrap to remove the leaching solution there from.

6. A method for recovering photographic film scrap having a cellulose acetate base which comprises washing the film scrap with warm water, then leaching it with a mixture of isopropyl alcohol and acetone containing 10-20% of the latter, at 68-110 F. under conditions whereby the scrap is not greatly softened and then washing the scrap to remove the leaching solution therefrom.

7. A method for recovering photographic film scrap having a base of a lower organic acid ester of cellulose which comprises washing the film scrap with warm water, then leaching it with a mixture of a lower aliphatic alcohol and acetone, in proportions which will swell the cellulose ester, at a temperature of 68110 F. under conditions whereby the scrap is not greatly softened.

8. A method for recovering photographic film scrap having a cellulose acetate base which comprises washing the film scrap with warm water, then leaching it with a mixture of methyl alcohol and acetone containing 10-20% of the latter, at 68-110 F. under conditions whereby the scrap is not greatly softened.

MARVIN J. REID. 

